In order to obtain the production of high-quality knitted fabrics, in today's knitwear manufacture it is essential that a specified amount of yarn required for stitch formation with strictly controlled yarn tension be fed to the needles of the knitting machines. Even the slightest yarn tension fluctuations may cause marked alterations in a stitch structure, which eventually result in the production of low-quality knitwear. Such yarn tension fluctuations may arise due to a variety of reasons, the major of which are as follows: a variation in the roll diameter, caused by the yarn turns being wound off and in the resistance of air as the diameter of the spool decreases; a variation in the level of friction between the yarn turns being wound off and the surface of the spool as a consequence of the decreased diameter of the spool; yarn nonuniformity, a variation in the coefficient of yarn friction, clogging of yarn guiding devices, variations in humidity and ambient air temperature, and a differing degree of wear of individual components of the knitting machines, etc.
The need for yarn tension stability has necessitated the development of devices for the feeding of yarn to the needles employing different operating concepts.
There are known a great deal of various devices for yarn feeding, in particular devices which provide for the positive feeding of yarn to the needles of knitting machines.
Known in the prior art is a device for guided feeding of yarn to a knitting machine (see U.K. Pat. No. 920527) comprising a roller, the surface of which is formed by pins mounted parallel to the axis of the roller in two flanges. The roller is driven by an endless band moving with a constant speed. The yarn being fed is trapped between the band and the pins of the roller.
A basic disadvantage of the aforementioned device consists in that the yarn is trapped between the roller pins and the band in an unstable manner, which leads to imparting yarn tension fluctuations to the knitting area and, therefore, results in a deteriorated stitch structure and uniformity of a knitted fabric, increased yarn ruptures and an reduced machine output.
Another essential disadvantage of the above device is the presence of one and the same yarn feeding speed in diverse knitting systems, which consequently limits the production potentialities of the machines.
Also known in the prior art is a device, wherein in order to expand the production potentialities of a knitting machine, yarn feeding rollers are arranged in a number of rows in height, with the rollers of each row being embraced by an individual drive band. The drive bands of each row move with different speeds and, therefore, yarn feeding to diverse knitting systems of the machine is also accomplished with different speeds.
This prior art device, like the one considered hereinabove, is not capable of fully compensating for yarn tension fluctuations, and the provision of yarn feeding to the diverse knitting systems of the machine accomplished at different speeds is made at the expense of considerable design intricacy, increased overall dimensions, which involves a substantial inconvenience when reloading, charging or changing yarn for the machine, as well as a reduced machine output associated therewith.
These disadvantages are partially obviated in a device comprising a yarn feeding roller provided with a single band drive having interchangeable pulleys for each yarn feeding device, and a yarn guide designed in the form of an inclined ring looping around the yarn feeding roller and having an inner diameter corresponding to the diameter of said yarn feeding roller (see F.R.G. Pat. No. 2,365,251).
The above device insures yarn feeding with variable speeds to diverse knitting systems of the machine by means of the selection of a suitable interchangeable pulley for each yarn feeding device. Such a device includes a set of nine interchangeable drive pulleys. When knitting various weave patterns, on each yarn feeding device there is mounted one of the nine drive pulleys. This device provides an opportunity for winding yarn on the rotating roller while it is being continuously consumed by the needles of the knitting machine in a concurrent manner. The placing of the yarn turns being wound on the yarn feeding roller surface is effected by means of setting the yarn turns downward with the aid of the inclined ring of the yarn guide. The roller is driven by an endless perforated belt.
Such a design of the yarn feeding device has a disadvantage consisting in the multiplicity of interchangeable pulleys, which is characteristic of the complexity and imperfection of the above yarn feeding device and its high materials consumption. Furthermore, the design incorporating the use of interchangeable pulleys of different diameters makes it necessary to install sliding idler pulleys intended to provide a required degree of belt tension, which additionally complicates both the structure and operation of the knitting machine.
Another disadvantage of the device lies in that the yarn guide is made dependent on the diameter of the yarn feeding roller and, hence, a change in the diameter of the roller causes a change in the diameter of the ring of the yarn guide. Such a design of the yarn guide also complicates the yarn feeding device in terms of its design and brings about some inconvenience in operating the knitting machines.
Still another tangible disadvantage of this prior art device consists in that it has a considerable mass of rotating components, as well as in that the yarn guide is conceived in the form of a rotating ring, which causes significant dynamic loads and the frequent yarn ruptures associated therewith.